Fluid coking process with quenching



FIG.-2

H. z. MARTIN ET'AL Filed. June so, 1954 FLUID COKING PROCESS WITH QUENCHINC FIG 'I April 14, 1959 Inventors United States Patent C i 2,882,206 FLUID COKINGPROCESS'WITH QUENCHING Homer Z. Martin, Cranford, and Charles E. Jahnig, Red Bank, N .J., assignors to Esso Research and Engineering Company, a corporation of Delaware Application June 30, 1954, Serial No. 440,318

2 Claims. (Cl. 202-37) The present invention relates to an improved coking process and particularly to a process for the thermal cracking and conversion of heavy oils, especially petroleum residua and the like. The conversion contemplated is carried out at least partially in liquid phase. The invention pertains more particularly to an improved method and apparatus for converting residual oils to volatile hydrocarbons and coke and includes the quenching of product coke, utilizing the thermal energy thereof to generate vapors useful in the process. The vapors so generated are used to assist, at least, in separating finely divided coke particles from coarser particles. The former are returned to the system while the larger particles are withdrawn therefrom.

It has been proposedrecently to convert heavy oils, such as petroleum residua, to more valuable products by contacting them, partly or largely in liquid state, with a fluidized mass of finely divided heat carrying solid particles. The hot particles are preferably quite inert catalytically although in some cases they may have some degree of catalytic activity. Such a process is described in some detail, for example, in an application of Pfeifier et al., Serial No. 375,088 filed August 19, "1953.

In the operation of a coking system of the type just referred .to, the conversion of the oil feed produces vapors of lower boiling point than the feed, and residual deposits of solid matter which settle and harden upon the solid heat carrying particles used for conversion. As a result the solid particles tend to grow in size by accretion of deposits. An optimum particle size range varies somewhat with the system chosen but ordinarily it is preferred to use heat-carrying solid particles largely between about 75 and 800 microns diameter. Average particle sizes usually range between about 100 and 250 microns, a preferred average being between 150 and 200, but there is always considerable spread in size range.

Due to deposits mentioned above, the particles not only grow in size but some of them also adhere together or 'agglomerate. Unless larger particles are constantly removed and replaced with small or seed particles, the system will rapidly become inoperative. Hence, as pointed. out in the application of Pfeiffer et al., it is necessary to withdrawmore or less continuously a stream of coarse particles and to return to the system finely divided seed particles to keep the operation in balance. As explained in greater detail in an application of Boisture et al., Serial No. 403,218, filed January ll, 1954, the number of seeds required should be equal to the number of coke particles withdrawn from the system (plus a suitable allowance forany agglomeration). The

weight of seeds varies inversely as the cube of product coke .size,.hence it is advantageous to withdraw coarse particles selectively.

The present invention is particularly concerned with an efi'icient elutriation process and apparatus for 'withp drawing the larger particles, which result from the nor- 2,882,206 Patented Apr. 14, 1959 mal growth process which takes place in the coking system, while returning the fine particles to the system.

Specifically, the invention contemplates the use, for

quenching, of a liquid which is vaporizable at temperatures below that of the particles withdrawn from the coking system. Thus, a stream of water in proportions of about 0.1 to 0.5 lb. per pound of withdrawn solids is injected, preferably continuously, into a fluidized mass of the solids being withdrawn. Where water is used, it is quickly converted to steam and the steam is used in a counter-current process to elutriate fine particles from the downflowing stream comprising fine and coarse particles approaching the withdrawal point. This system, may be called a quench-elutriator since it results in quenching the coarse particles withdrawn, and elutriating from the withdrawn particles the finer particles which are returned to the system. A specific type of quenchelutriator has already been described in the application of Spitz et al., Serial No. 424,668, filed April 21, 1954. The present invention is generic in some respects to that described in said Spitz et al. application and the present case also covers specific variations thereof.

The invention and its objects will be more clearly understood by referring to the attached drawing wherein Figure 1 shows diagrammatically a coking system of the general type to which the invention is applicable;

Fig. 2 shows on a greatly enlarged scale the quenchelutriator apparatus in one form, and

Fig. 3 shows another form or variation thereof.

Referring first to Fig. l, the system therein shown is generally similar to that of the Pfeiffer et al. application. Briefly, a coking vessel 11 having a relatively long and tapered or conical bottom section 13 is supplied with hot solid particles which may be sand, beads, refractory granules of various types etc., but is preferably of coke formed in the process. This is supplied through line 15. Coke flows into line 15 from a standpipe 17 which may be controlled by a valve 19. A heater vessel 21 contains a mass, preferably a fluidized bed of the inert particles, and is supplied with combustion gas or air through an inlet 23. Instead of a fluid bed heater 21, a transfer line heater may be substituted if desired. Fuel gas may be fed through a line 24 for starting up, or for heating when it is desired to minimize combustion of the coke.

The solid particles, for example coke granules of .a size ranging from about to about 800 microns diameter more or less, are heated to a temperature of about 1000 to 1300 F., more or less. The hot solid particles which flow to the coker through line 15 supply the necessary heat for converting the oil which is fed through a set of nozzles 25, 27, 29, connected to a manifold 31. By reason of the conical shape of the reactor, only a small amount of fluidizing vapor or gas is needed at the bottom thereof, the bulk of the fluidizing requirements being supplied by vaporization and/or cracking of the oil feed introduced at various levels throughout the conical section. This minimizes steam consumption and overhead exchanger sizes. 7

Although, as indicated above, various particulate solids may be employed to supply the necessary thermal energy for pyrolysis or coking, it is preferred to use coke granules produced in the process. It will be understood that reference hereafter to coke is exemplary and that sand and other inert heat-carrying particulate materials mentioned above may be substituted for the original charge of solids or may be added when needed.

The coking vessel 11, filled to an appropriate level as indicated at 33 with coke or other inert particles, is kept fluidized by adequate gas of vapor flow. The oil to be converted is fed thereto largely or entirely in liquid phase, through the nozzles 25, etc., previously mentioned and is converted by the heat of the solids to vapors and to coketionated above the scrubber in section 39 as also shown in the Pfeiflfer et al. application, Serial No. 375,088. "In order to minimize formation of coke deposits in the apparatus, a stream of hot solids may be directed through line 41 into the outlet section at the top of the coker.

The individual solid particles which constitute the coking bed gradually grow in size because of the layers of coke forming thereon and they tend to lose their mobility and fluidity in the fluidizing vapors passing upwardly therethrough. Moreover, they are cooled down in the coking process. Therefore a stream of particles is withdrawn, preferably at a more or less uniform rate, through a standpipe '45, preferably under control of a valve 4'] and through an elbow or reverse bend 49 into a riser 51.

By injection of lifting and aerating gas, for example, steam or air on the riser side, this stream of solids is returned to the heater 21 where combustion, or partial combustion,

takes place to reheat them. It is not necessary, however,

to return all of the particles since they are increasing in total mass as a result of the coke formed by cracking in reactor 11. Hence, part of the solids, i.e. coke, may be withdrawn as product through a stripping section 55 at the bottom of the conical coker section 13. A stripping gas such as steam may be introduced through a line 57, the solids passing downwardly into a quench-elutriator section 59 below the stripper 55.

Referring now to Fig. 2, the stripper 55 is shown on a much larger scale, as are the other parts to be described. Below the stripper, the quench-elutriator 59 is situated, preferably being provided with a bafi le arrangement 61. As shown in Fig. 2, this baflle means consists of disc and donut or shed type batfles. The purpose of this baflle arrangement is to prevent undue mixing of the quenched solids with the unquenched particles in the stripping zone. I

It also gives countercurrent contacting in the quenchelutriator. Other baflle types can be used, such as perforated plates, packing, etc. Steam passes upwardly from the quench-elutriator 59 into the stripper 55, while stripped coke flows down into the elutriator to outlet 69.

Baflies 61 are designed to allow the desired downflow of coke.

The quench-elutriator section, of smaller horizontal cross-section than the main reactor, may be provided with steam inlet 63, to assist in fluidizing the solids therein, but 7 fiuidizing is preferably accomplished entirely, or almost entirely, by injection of vaporizable liquid at a point near thebottom of quench-elutriator through an inlet line 65. The preferred liquid is water which, of course, is converted immediately to steam since the temperature of the solids coming from the coking zone is usually at least 750 F. The water is injected as a steady small stream to cool the product coke to somewhat above the water boiling point. The water may be equivalent to 0.1 to 0.5 lb. per pound of solids withdrawn from the system. The control valves 66 and 69 are adjusted to proportion the water feed to the stream of coke withdrawn. The steam thus produced is of considerable volume and it has suflicient velocity to elutriate from the quench-elutriator the fine particles which are carried up through bafiies 61 with the steam. Coarse particles are Withdrawn as product. The latter, in a typical case, comprise from30 to 85% of the total solids fed to the elutriator and the fines are returned to the stripper along with the steam.

" About 15 to of the coke produced is normally burned to supply the thermal requirements. Where larger coke production is desirable an extraneous fuel may be fed to the heater through line 24, and burned preferenjtially to the coke as is known in the art. In this case the total coke product may ultimately be withdrawn.

The coarse quenched coke particles, from which the fines have been elutriated, pass downwardly by gravity through a valve 67 in the outlet line 69.

Referring now to Fig. 3, a modification is shown wherein the quench-elutriator is incorporated in an outlet line 73 from the heater vessel 21 instead of the coker vessel. Coke flows down through line 73. A perforated grid 74 is shown, but other baflies maybe used and are preferably incorporated as shown at 75. These consist of a series of disc and donut bafiies of known' types. Their purpose is the same, namely, to prevent undue mixing of quenched solids with the unquenched solids at a higher level. As shown in Fig. l, the solids to be circulated. for supplying the thermal requirements of the coker are drawn from the burner through line 71 without quenching and returned to the coker through lines 17 and 15. A product coke stream is drawn off through line 73 (Fig. 3) and passed downwardly into the quench-elutriator valve 76 into section 77 to which a stream of quenching liquid, preferably water, is supplied through line 78 under control of valve 79.

The operation is similar to that described in connection with Fig. 2 above. The fine particles are carried upwardly with the steam generated as the result of quenching, and are returned toburner 21. The cool coarser particles flow downwardly through outlet line 81' which may be equipped with a valve 82. In Fig. 3, grid-74 prevents mixing of solids between elutriator 77 and burner 21. Coke flow into the elutriator is controlled by valve 76 and the elutriator can be operated as a dilute phase, if desired. The systems of Figs. 1 and 2 operate better in dense phase. 7

It will be understood that instead of water a low boiling hydrocarbon liquid may be used on the reactor side (Figs. 1 and 2) as the quenching medium, or any other liquid of appropriate boiling range which vaporizes completely or substantially completely and which furnishes an elutriating gas or vapor for returning the desirable fine particles to the system.

It will be also understood that the quench-elutriator may be associated either with the coking side or the burner or heater side or with both, or it may be inserted at any appropriate point in either or both of the transfer lines. Inflammable quench fluid, of course, would not be used on the burner side. The essential feature of the present inventionis that the downwardly flowing coke-coated solids are contacted with a suitable quantity of vaporizable liquid to quench them to a temperature suitable for further handling as product. The vapors so produced are utilized to return to the system the fine particles which serve as seed or nuclei for the deposition of coke formed in the system, so that they thereby grow to larger size before being withdrawn as product. In addition, extraneous seed particles are added as needed to control particle size in the system.

It will be obvious that various changes and modifications may be made within the scope of the invention 'as will occur to those skilled in the art. For example, the quench-elutriator unit per se may be a separate vessel. Vapors from the elutriator may be returned to the reactor for aeration or stripping, or may be used for heating, etc., as desired.

The system can also be applied to other processes such as coal coking, ore or mineral processing, shale retorting, coke calcining or activation, etc. In the latter case, the product solids may be separated into fine and coarse fractions for separate handling.

For example, the fines may be returned to the system to improve fluidization, while the coarse solids can be withdrawn as product. This technique makes it possible to operate with a coarser size of feed solids, and still maintain a large amount of fines in the circulating system. The steam generated by quenching can be used in the process for reaction with coke, after removing fine product solids.

What is claimed is:

1. In a fluid coking process wherein a heavy oil is converted by contact with finely divided coke particles having a size in the range of 75 to 800 microns maintained as a dense turbulent fluidized coking bed at a coking temperature in a coking zone, thermal energy for conversion being supplied by circulation of coke particles from said coking zone to a heating zone and then back to said coking zone, the improved method of withdrawing and quenching the net coke product of said process as selected relatively large size particles which comprises maintaining a vertically elongated quenchelutriation zone below and integrally aflixed to said coking zone through a path of fluid communication, maintaining a dense turbulent fluidized quench bed of coke particles in said quench-elutriation zone, injecting 0.1 to 0.5 lb. of water/lb. net coke product into said quench bed, said quench bed being maintained at a temperature above the boiling point of water whereby a considerable quantity of steam is formed, flowing coke particles substantially at the coking temperature from said coking bed downwardly through said path in disperse phase While flowing said steam upwardly therethrough at a velocity sufiicient to entrain relatively fine coke particles whereby only relatively coarse coke particles reach said quench bed, and withdrawing from said quench bed, a relatively coarse coke product amounting to to of the coke particles withdraw from said coking bed.

2. The improvement of claim 1 wherein baffles are placed in said path of fluid communication to promote countercurrent contacting between said steam and coke particles therein, and to prevent undue mixing of quenched and unquenched particles.

References Cited in the file of this patent UNITED STATES PATENTS 2,366,057 Russell Dec. 26, 1944 2,506,317 Rex May 2, 1950 2,581,041 Ogorzaly et al. Jan. 1, 1952 2,606,144 Leffer Aug. 5, 1952 2,608,526 Rex Aug. 26, 1952 2,614,069 Matheson Oct. 14, 1952 2,639,263 Leifer May 19, 1953 2,661,324 Leifer Dec. 1, 1953 2,699,421 Borgerson Jan. 11, 1955 2,701,787 Hemminger et al. Feb. 8, 1955 2,707,702 Watson May 3, 1955 

1. IN A FLUID COKING PROCESS WHEREIN A HEAVY OIL IS CONVERTED BY CONTACT WITH FINELY DIVIDED COKE PARTICLES HAVING A SIZE IN THE RANGE OF 75 TO 800 MICRONS MAINTAINED AS A DENSE TURBULENT FLUIDIZE COKING BED AT A COKING TEMPERATURE IN A COKING ZONE, THERMAL ENERGY FOR CONVERSION BEING SUPPLIED BY CIRCULATION OF COKE PARTICLES FROM SAID COKING ZONE TO A HEATING ZONE AND THEN BACK TO SAID COKING ZONE, THE IMPROVED METHOD OF WITHDRAWING AND QUENCHING THE NET COKE PRODUCT OF SAID PROCESS AS SELECTED RELATIVELY LARGE SIZE PARTICLES WHICH COMPRISES MAINTAINING A VERTICALLY ELONGATED QUENCHELUTRIATION ZONE BELOW AND INTERGRALLY AFFIXED TO SAID COKING ZONE THROUGH A PATH OF FLUID COMMUNICATION, MAINTAINING A DENSE TURBULENT FLUIDIZED QUENCH BED OF COKE PARTICLES IN SAID QUENCH-ELUTRIATION ZONE, INJECTING 0.1 TO 0.5 LB. OF WATER/LB. NET COKE JPRODUCT INTO SAID QUENCH BED, SAID QUENCH BED BEING MAINTAINED AT A TEMPERATURE ABOVE THE BOILING POINT OF WATER WHERBY A CONSIDERABLE STANTIALLY AT THE COKING TEMPERATURE FROM SAID COKING BED DOWNWARDLY THROUGH SAID PATH IN DISPERSE PHASE WHILE FLOWING SAID STEAM UPWARDLY THERETHROUGH AT A VELOCITY SUFFICIENT TO ENTRAIN RELATIVELY FINE COKE PARTICLES WHEREBY ONLY RELATIVELY COARSE COKE PARTICLES REACH SAID QUENCH BED, AND WITHDRAWING FROM SAID QUENCH BED, A RELATIVELY COARSE COKE PRODUCT AMOUNTING TO 30 TO 85% OF THE COKE PARTICLES WITHDRAW FROM SAID COKING BED. 